The present invention relates to antennas, and, in particular, relates to microstrip patch antennas.
Designs for currently available printed antennas (electromagnetic waves radiating structures) make use of thin films of good conductors such as copper and gold. The thin film conductors are deposited, printed, or etched onto thin, low loss dielectric substrates which are usually backed by another good conductor. The thickness of the good conductor on top of the dielectric substrate is several times the conductor's skin depth. This is done to minimize the conductor loss. The usual thickness range from 0.5 to 2.0 mils (12 to 50 microns). A typical microstrip patch antenna configuration is shown in FIG. 1.
These types of antennas have been studied extensively. A recent publication, Handbook of Microstrip Antennas, vol. 1 and 2, edited by J. R. James and P. S. Hall, Perigrinus Press, UK, 1989, is a comprehensive overview of the current state-of-the-art and is incorporated by reference. Various versions of the configuration shown in FIG. 1 are used in practice. The most commonly-used shapes include rectangles, circles, and triangles. The most common methods of exciting the patches are via a vertical probe which is fed through the ground plane, or via a microstrip line on the top surface of the dielectric substrate.
These microstrip patch antennas are usually used as elements of array antennas. The most common applications for these antennas are on aircraft, satellites, missiles, telemetry systems, battlefield surveillance systems, domestic DBS receivers, reflector feeds, and convert antennas.
The disadvantage of currently available microstrip patch antennas is their narrow radiation bandwidth. Typical bandwidth values range between 1 and 4%. The bandwidth is inversely related to the Q-factor of the patch's equivalent cavity. Several approaches have been made to increase the bandwidth of these patch antennas but each attempt introduces some new disadvantage. For example, increasing the substrate height does increase the bandwidth but it also increases the excitation of surface waves and radiation from the feed lines, both undesirable side effects. Another approach utilizes multiple patches which are stacked vertically at different levels in the substrate. This approach increases fabrication difficulties and hence the cost of the antenna. Also, in both of the above approaches, the total thickness of the antenna is increased which reduces its utility in low profile operations.